The NIL (NanoImprint Lithography) technology has been developed as a technique that enables to form a microstructure of a semiconductor. In order to inspect a template of the NIL technology, an image of the template is taken with a SEM (Scanning Electron Microscope) and a shape defect such as a rupture or a bridge (short-circuit) in the microstructure or a critical defect such as a thickening or thinning of the line width is detected. Defect detection with a wafer inspection apparatus using a structure actually transferred on a wafer is also performed.
However, in these methods, imaging takes a long time, or a detected defect cannot be always determined as a defect of the template because a result having subjected to a manufacturing process on a wafer is inspected. Therefore, these methods have a problem when used for the template inspection on a full scale.
Meanwhile, trials of imaging a template with an inspection apparatus used in an inspection of a photomask and detecting a defect on the template based on the image have been conventionally performed (see Patent Literature 1, for example). In a current downscaled technology node, the dimension of the microstructure of a template is minuter than a light source wavelength of the inspection device and the inspection device cannot resolve the microstructure.
That is, when an image is taken with the inspection apparatus, a microstructure of a template that is periodically repeated as in a memory cell region is not resolved and is observed to have substantially uniform luminance of a gray level between a white level and a black level. If such a microstructure that is periodically repeated has a defect, the periodicity of repetitive patterns in an image of the microstructure is disturbed and a luminance change occurs in the image of the gray level according to the degree of the defect. The inspection apparatus detects such a luminance change caused by disturbance in the periodicity based on comparison between images, thereby detecting a defect in the microstructure that is unresolvable.
However, the luminance values of the gray level change according to the dimension of the repetitive patterns or the dimensional ratio thereof. Therefore, if the dimension or the dimensional ratio of the repetitive patterns varies within the plane of a template, the luminance values of the gray level also fluctuate correspondingly. In this case, the gray level serving as a reference differs between comparison images, which causes a problem that it is difficult to detect a defect.